a) Field of the Invention
The invention relates to a device for measuring the stickiness of a flowable medium, in particular a printing ink, which is led as a layer between two surfaces that can be moved in the same direction, through a convergence zone, a pressure zone and a divergence zone, it being possible to use a measuring device to measure, as a measure of the stickiness, that force which is needed to separate the surfaces from each other.
In this case, the term stickiness is interned to include, in particular, the tack-and other rheological properties, such as viscosity.
b) Description of Related Art
In a device of this type disclosed by DE-A-19 00 328, the flowable medium to be tested is brought, in an accurately metered quantity, between two rotatable bodies, of which one is driven and the other is carried along by a frictional connection. In this case, a lever arrangement is used to measure the force which is necessary to separate the two bodies from each other. This device has the fundamental disadvantage that, as a result of driving only one rotatable body and carrying the second rotatable body along via the flowable medium to be measured, shear forces occur in this medium, which lead to a change in the rheological properties of the medium to be tested, which results in the set force for determining the tack which, during its measurement, is intended to be perpendicular to the two surfaces between which the medium to be measured is located, is falsified. A further disadvantage of this and other known devices is basically that, during the testing of printing inks and their lithographic properties, no account can be taken of those influences which result, for example, during the application of the flowable medium, for example a printing ink, to paper or other materials, since the device comprises two rotating bodies with metal and/or rubber surfaces but that, for example, the preconditions prevailing in a printing machine cannot be simulated with such a device. Furthermore, it is not possible either to determine the influence of the layer thickness of the applied medium as a function of the material of the surfaces on the tack value. Nor is there any possibility of establishing the superimposition, taking place during multicolor printing, of various flowable media, with regard to their influence on the tack. All such testing possibilities are impossible with this known device and also further devices which have been disclosed.